Low overhead elevators have become increasingly popular. As opposed to traditional elevators which include motors, governors, and associated cabling in a machine room at the top of vertical hoistways in which the elevators move, low overhead elevators do not require placement of such components at the top of the hoistways. For example, some low overhead elevators may provide the driving force through machines located above the elevator roof but without the provision of a machine room. In so doing, such low overhead elevators conserve valuable space in the commercial and residential buildings in which they operate.
When a service technician wants to inspect or service the pulleys, hoisting cables, guide rails, machine controls or any other device at the upper end of the hoistway, he or she usually needs to do so on top of an elevator car. The cars may be designed to slowly approach the desired locations, such as by using a control system as disclosed in a co-pending application published as WO 2008/004022. In order to maintain the safety of the technician, extra preventive measures have been developed to stop the upward movement of the car as it approaches the top of the hoistway to provide ample space for the technician. This is particularly important in the case of low overhead elevators, in which there is less clearance between the top of car and the top of the hoistway.
One of the preventative measures is a retractable stop provided at the pit floor of the elevator system to block further downward movement of a counterweight when deployed. An example of this is disclosed in another co-pending application published as WO 2008/002300. As the counterweight is operatively connected to the elevator car, stopping downward movement of the counterweight necessarily stops upward movement of the car. When the elevator operates under normal mode, the stop is retracted to allow the counterweight to downwardly extend to its full range.
When deployed, a triangular support structure is formed among a horizontal strike plate, an oblique stop member and a vertical mounting channel, in which the horizontal impact plate blocks the downward movement of the counterweight with the impact force transmitted into the pit floor through the mounting channel and support member. However, the triangular configuration necessarily requires the support member to bear some horizontal vector of the impact force. As a result, the support member has to be constructed with sufficient lateral dimension and heft to provide the needed structural rigidity.
Meanwhile, the dimensions and location of the elevator car and counterweight are restricted by the limited space within the hoistway. In order to maintain safe operation of the elevator car in its full range, a minimum clearance (e.g. 25 mm) is required between the fully retracted stop and counterweight to accommodate any incidental horizontal movement of the counterweight within the hoistway. However, because of its relatively thick lateral profile necessary to maintain adequate structural rigidity, the existing stop may fail to meet the minimum clearance requirement. One solution is to create a longitudinal groove on the surface of the counterweight (including the counterweight frame and counterweight filler) that faces the retractable stop to provide the extra clearance. While effective, this necessarily requires modification of the existing elevator system or creation of a specifically configured counterweight, either of which adds significant expense to the design.
Hence, there is a need for a retractable stop with an improved lateral profile that meets the minimum clearance requirement when used with a conventional counterweight without imparting significant additional cost. Moreover, there is a need for a retractable stop that has an improved lateral profile in a retracted position without sacrificing the load bearing capacity in a deployed position.